The present invention relates to systems for detecting electrical signal pulses and, more particularly, for detecting pulses subject to varying peak amplitudes.
Electrical pulses, that is, substantial changes in magnitude level of an electrical variable over a relatively short time, are generated during the operation of various electrical devices and are often used to transmit information. One such device is a sonic waveguide based relative translation distance measuring system, or instrument. In such system, an electrical current pulse is applied through an electrical conductor wire encased in a ferromagnetic magnetic material waveguide tube, or alternatively, through a ferromagnetic material electrical conductor rod that also serves as the sonic waveguide. An external magnet, serving as a position marker by being guided along the tube to have a position there along that is dependent on the distance to be measured, provides a magnetic field which interacts with the translating magnetic field established by the current pulse applied through the wire or rod. That interaction results in a torque on the waveguide, whether tube or conductor, at the location of the interaction to thus provide a torsion pulse at that location in the sonic waveguide that is transmitted along that waveguide including back toward the source of the current pulse. The time duration between the initiation of the current pulse and the receiving of the sonic pulse reaching a sensing location at the sensing end of the waveguide is a measure of the distance to the variable position magnet from that location.
Such current pulses in the wire or guide in the relative translation distance measuring system are repeated frequently to provide a continual update of the position of the marker magnet, and so the distance thereto. The current pulse must be of a sufficient magnitude to generate the necessary magnetic field for interacting with the magnetic field of the varying position marker magnet so as to cause a sufficient torsion pulse to result therefrom in the waveguide at the marker position to form a traveling sonic pulse returning on that waveguide of a sufficient magnitude to be detected. A typical detection mechanism is to have the sonic pulse, or transmitted torsion pulse, move along magnetostrictive solenoidal cores that are attached to the waveguide and positioned in a magnetic coil to form a mode converter, thereby generating a voltage output corresponding to such sonic pulse induced motion.
Unfortunately, electrical noise due to various sources is also generated leading to many other pulses appearing in the voltage output over time, many of which have an amplitude less than that of the signal pulse induced by the torsion wave. Thus, these other pulses can be discriminated against on a magnitude basis to thereby select out only, or nearly only, those pulses due to the torsion waves. However, this situation is further complicated by the traveling sonic waves having magnitudes which decrease with distance along the sonic waveguide. Those which start further away will have a lower peak magnitude than those which are started closer to the mode converter. Thus, discrimination between electrical pulses at the output of the mode converter by magnitude can be difficult when done by a fixed magnitude threshold detector because of the difficulty in selecting a threshold value that would be proper for electrical pulses converted from sonic waves based on torsion pulses which are generated near the mode converter versus those which are generated far from the mode converter.
In addition, this selection process is complicated still further by the desire to use the same pulse detector circuitry in various instruments since the waveguides will be much longer in some instruments than in others leading to the magnitudes of the electrical pulses varying even more in peak magnitudes at the mode converter because of the greater range of distances over which torsion pulses can be generated. Furthermore, the sensing arrangements in each such instrument will significantly in sensitivity to returning sonic pulses in the same conditions even with the same pulse detection circuitry being used in instruments. Finally, the magnetostrictive constants of the magnetic materials used in the waveguide and the converter will vary significantly with temperature thereby also causing significant differences in pulse magnitudes. Thus, there is a desire for a signal pulse detection system which can detect signal pulses having peak amplitudes which substantially vary over time in the presence of noise.